Manufacture of paper embodying alkaline earth metal carbonate fillers



Patented Mar. 5, 1935 UNITED STATES PATENT QFFICE MANUFACTURE OF PAPEREMBODYING ALKALINE EARTH METAL CONATE rmnns No Drawing. ApplicationFebruary 28, 1933, Serial No. 658,942

Claims.

This invention relates to the manufacture of paper and it has particularapplication to the sizing and filling of paper wherein alkaline earthmetal carbonate fillers are employed.

Alkaline earth metal carbonates, notably calc i um carbonate, have beenproposed as fillers for paper heretofore and have been utilized to someextent for this purpose. However, their use has not met with favor inconnection with a rosin- 10 alum or similar size, due to theunsatisfactory quality of the resulting paper'product. It has generallybeen considered that the alkalinity of the carbonates functions todestroy or seriously impair the rosin-alum size. As a result, it hasbeen almost universal practice to utilize other fillers, particularlyclay, whichis relatively inert under the acidic conditions developed inthe sizing of paper with alum. I

Clays which have a sufiicient degree of whiteness are relatively rareand correspondingly expensive. On the other hand, carbonates, andparticularly calcium carbonate, of a satisfactory quality so far ascolor and degree of fineness are concerned, are available in almostunlimited quantities and at a cost which is substantially less than thecost of clay. For this purpose naturally occurring carbonates which havebeen reduced to the desired degree of fineness by trituration orotherwise, as well as artificial carbonates such as precipitated chalkor the byproduct of causticizing processes such as are commerciallyemployed in the manufacture of caustic soda for use in the manufactureof soda pulp, may be used. Moreover, it is fairly generally held thatthe deterioration of paper is accelerated by acidic conditions such, forexample, as may be brought about by the use of a large proportion ofalum, and that a reduction of acidity brings about a correspondingincrease in life of the paper.

In view of the foregoing, as well as other factors, many proposals havebeen made with the -view of minimizing or obviating undesirablemodifications of these ideas have been proposed, but none to date hasbeen satisfactory.

The object of the present invention is to provide a method of sizing andfilling paper using alkaline earth metal carbonates, and particularly 5calcium carbonate, as a filler, whereby the shortcomings anddisadvantages of the prior processes are overcome; whereby a carbonatesuch as is readily available on the market may be employed withoutpreliminary treatment; equipment such as is already installed in thestandard paper plants may be utilized without extensive or expensivealterations; whereby a paper of a quality, particularly as regards lifeand resistance to ink penetration are concerned, 15 is at least as goodas corresponding grades of present day paper; and finally, whereby thecost of sizing and filling paper is reduced below the cost of paperwhich has been filled with present day fillers, notably clay.

According to the present invention, the wood or textile fibers ormixture of the two are formed into a pulp of the usual workingconsistency and freeness, thereafter arosin size, for example, isintroduced and thoroughly distributed therein. Subsequently, suflicientalum is added to precipi tate the size. Under these conditions, ifcalcium carbonate were introduced or present, it would destroy the sizeand a paper of unsatisfactory quality would be obtained. In practicingthe present invention,.c2irbon dioxide, or a gas or reagent containingcarbon dioxide, is introduced into the mix and an equilibrium conditiontherewith is attained or approximated by thorough agitation orintermingling. Thereafter the carbonate filler may be introduced with noapparent deteriorative or destructive action on the size. The filler isthen thoroughly distributed throughout the pulp mixture and a solublebase such as soda ash is added, after which the batch is againthoroughly mixed and finally formed into sheets in the usual manner.Under some conditions the resulting paper product may be found tocontain filler spots. This shortcoming may, however, be easily andcompletely overcome by substituting for the soda ash prescribedhereinabove a doc of aluminum hydroxide, which preferably should bedistinctly basic. To this end one may add alum and soda ash to thebeater whereby the floc is formed in the beater, or, the fioc may beformed in separate vessel and subsequently added to the beater. Verysatisfactory results, both from the standpoint of convenience andquality of product, have been obtamed by the use of sodium aluminate inlieu whereby the m .of the soda ash-alum floc.

This material not only provides the desired alkalinity, but alsosupplies the necessary alumina for the production of the aluminumhydroxide floc.

The presence of the carbon dioxide-which, incidentally, shouldpreferably be kept in contact with the mixture as long as the mixtureundergoes vigorous beating or agitation under conditions whereby thedissolved carbon dioxide might be expelled and the proportion thereofthereby reduced materially, appears to act as an impediment or inhibitorto the destructive action which would otherwise take place upon theintroduction of the carbonate filler into the pulp containing the rosinand alum size. It has been observed in a number of experiments that thepH value of the contents of the beater varies from 6.2 to 7.2 whencarbon dioxide is utilized in conjunction with the calcium carbonatefiller. On the other hand, when the carbon dioxide is omitted, the pHvalue of the contents of the beater is approximately 7.8 to 9.0. Underthese latter conditions, no appreciable sizing. has been observed. Thepresence of the carbon dioxide reagent, therefore, functions to maintaina pH value at which the alkalinity or acidity of the batch is such as torealize good sizing without inducing the destruction of the size, whichappears to be brought about at the higher pH values that are observedwhen no carbon dioxide is employed.

The source of the carbon dioxide reagent is optional, and one mayintroduce pure gaseous carbon dioxide, solid carbon dioxide, or flue gaswhich is high in CO2 content, for the purpose of maintaining the desiredpH value or otherwise rendering the calcium carbonate passive to thesize.

The addition of the alkaline floc or floc producing agent, following theaddition of the filler, and for this purpose sodium aluminate ispreferred, as compared to other basic mixtures, insures a uniformly wellsized sheet having inordinately good ink penetration qualities. Theproduct thus obtained has been found to have an ink penetration of from5 to 7 minutes when tested under the usual conditions for this test.

A specific example of one embodiment of my invention is hereinafter setforth:

One hundred twenty-five parts (by weight) of sulfi te pulp aredistributed in 7000 parts (by weight) of water by means of a beater ofstandard design to the usual or ordinary degree of freeness, after which2.5 parts of rosin size (2% on the basis of the air-dried pulp) areintroduced in the usual dispersed condition and evenly distributed bycontinuing the beating operation for 15-20 minutes. Two and one-halfparts of commercial paper makers grade alum (2% on the basis of theair-dried pulp) are added and the beating operation is continued for anadditional period of 15-20 minutes.

Carbon dioxide is then introduced until the solution appears to besaturated. This may be introduced from a cylinder or as solid carbondioxide. After this. 43.75 parts of calcium carbonate filler (35% on thebasis of the air-dried pulp) are added and uniformly distributedthroughout the batch in the usual manner. To the resulting mixture thereis then added one part of soda ash (.8% on the basis of the airdriedpulp). After 15 minutes of mixing, the pulp is removed from the beaterand formed into sheets. In lieu of soda ash, one may add one part ofcommercial sodium aluminate (80-85% NazAnoo, (3% on the basis of the Yair-dried pulp). Sheets produced in the usual manner from this mixturehave unusually satisfactory properties both as regards uniformity andink penetration.

Obviously, the foregoing procedure may be varied as to the size ofbatch; as to the relative amount of water, which, it is to be noted, maybe reduced substantially from that specified to approximate more closelythe ratio commonly employed in paper mills; as to the method of formingthe sheet; the ratio of ingredients employed; and the precise conditionsof operation as above set forth. The several steps of adding reagents tothe pulp may be effected in a single beater or progressively insubsequent stages of the progress of the pulp to the sheet-formingmachine; thus, for example, the alkaline floo may be added to themixture in the stuff chest.

Moreover, the addition of other ingredients such as dyes,lpigments, andother agents, commonly employed in the manufacture of paper, includingclay, may be incorporated without departing from the spirit of thepresent invention, it being understood that the specific conditions areexemplary only. Similarly, other sizing agents, such as the stearates,may be substituted for the rosin size.

What I claim is:

1. A method of sizing paper wherein an alkaline earth metal carbonate isemployed as a filler and in combination with a size consisting of rosinand alum, that comprises introducing the rosin size and alum and addinga carbon'dioxide reagent before adding the carbonate filler.

2. A method of sizing paper wherein an alkaline earth metal carbonate isemployed as a filler in combination with a rosin size and alum, thatcomprises introducing the rosin size and alum to precipitate the size,adding a carbon dioxide reagent before adding the carbonate filler, andfinally, adding a soluble basic material before forming the film.

3. A method of sizing paper wherein an alkaline eartlr metal carbonateis employed as a filler in combination with a rosin size and alum,thatcomprises, first, introducing the rosin size and alum to precipitate thesize, subsequently addsize and alum to a pulp, subsequently introducingcarbon dioxide into the aqueous suspension, thereafter adding a calciumcarbonate filler, and finally adding sodium aluminate before forming thepaper sheet.

5. In the manufacture of paper wherein a rosin size and a calciumcarbonate filler are employed, the step which consists in maintaining apH value of approximately 6.2-7.2 by means of carbon dioxide during andsubsequent to the addition of calcium carbonate to the pulp containingthe rosin-alum size.

6. The method according to claim 5 and further characterized in that abasic floc is added to the resulting mixture before forming the papersheet.

7. The method as defined in claim 5 and further characterized in thatsodium aluminate is added to the resulting mixture before forming ciumcarbonate filler to the resulting mixture while maintaining a pH valueof the pulp me dium of approximately 6.2-7.2 by means of carbon dioxide,subsequently adding a relatively small quantityof sodium aluminate ascompared to the amount of size and alum employed, and finally formingthe paper sheet.

9. The method of sizing paper wherein an alkaline earth metal carbonateis employed as a filler in combination with a sizing material, the stepwhich comprises maintaining the said aqueous medium charged with carbondioxide havin a pH value 0! approximately 6.2-7.2 during the addition ofthe carbonate filler to the pulp mixture.

10. In the manufacture of paper wherein a rosin size and a calciumcarbonate filler are employed, the step which comprises maintaining thepH value not substantially greater than 7.2 during and subsequent to theaddition of the carbonate filler to the pulp mixture by the ad ditionthereto of carbon dioxide.

COLVER P. pm.

